Compositions for waving of hair contain a reducing agent for breaking the disulfide bonds in hair, thereby allowing the hair to be permanently reshaped. U.S. Pat. No. 4,158,704 teaches methods for waving of hair using compositions containing thioglycolate compounds as the reducing agents. Thioglycolate compositions produce waving of hair that typically lasts about 3 to 4 months. However, mercaptan or thioglycolates produce a strong unpleasant odor.
U.S. Pat. No. 5,338,540 teaches hair waving compositions containing a sulfite and/or bisulfite reducing system, urea, and a cationic polyquaternary resin, which purportedly yield a hair waving or straightening effect equivalent to thioglycolate compositions without the unpleasant odors associated with thioglycolate. Bisulfite compounds produce a waving of hair that is shorter in duration, i.e., lasting from about 1 to 2 months. Bisulfites, however, are known to strip color from artificially colored hair.